Affiliation

Abstract

Strains of Lactococcus lactis isolated from plant tissues possess adaptations that support their survival and growth in plant-associated microbial habitats. We previously demonstrated that genes coding for a hybrid nonribosomal peptide synthetase/polyketide synthase (NRPS/PKS) system involved in production of an uncharacterized secondary metabolite are specifically induced in L. lactis KF147 during growth on plant tissues. Notably, this NRPS/PKS has only been identified in plant-isolated strains of L. lactis. Here, we show that the L. lactis KF147 NRPS/PKS genes have homologs in certain Streptococcus mutans isolates and the genetic organization of the NRPS/PKS locus is conserved among L. lactis strains. Using an L. lactis KF147 mutant deficient in synthesis of NrpC, a 4'-phosphopantetheinyl transferase, we found that the NRPS/PKS system improves L. lactis during growth under oxidative conditions in Arapidopsis thaliana leaf lysate. The NRPS/PKS system also improves tolerance of L. lactis to reactive oxygen species and specifically H2 O2 and superoxide radicals in culture medium. These findings indicate that this secondary metabolite provides a novel mechanism for reactive oxygen species detoxification not previously known for this species.

Growth of L. lactis KF147 and BAL1 in ATL with paraquat. L. lactis KF147 and BAL1 were inoculated into 10 ml ATL containing 10 mmol/L paraquat and incubated at 30°C without aeration. The average ± SD of three replicate cultures is shown

Figure 3

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Growth of L. lactis KF…

Figure 3

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Growth of L. lactis KF 147 and BAL 1 in GM 17 under…

Figure 3

Growth of L. lactis KF147 and BAL1 in GM17 under respiratory conditions with and without paraquat. L. lactis KF147 and BAL1 were inoculated into GM17 under respiratory conditions (continuous aeration and 10 μg/ml hemin) (a) or respiratory conditions and 20 mmol/L paraquat (b). Bacteria were incubated at 30°C in microtiter plates and OD was measured at 600 nm. The average ± SD of at least eight replicate cultures is shown